INVESTIGATION OF IMPULSIVELY-STARTED FLOW AROUND SIDE-BY-SIDE CIRCULAR-CYLINDERS - APPLICATION OF PARTICLE IMAGE VELOCIMETRY

The impulsively-started flow held for two and three circular cylinders of equal diameter arranged side-by-side has been investigated using p article image velocimetry (PIV), over a transverse pitch ratio range o f T/D =1.0-3.0, and for Reynolds numbers from Re = 1500 to 3000. The P IV technique was used to obtain a time history of the instantaneous in -plane vorticity field from the moment of impulsive start, from which the development of the flow was studied. Measurements of vortex streng th and vortex position relative to the cylinders were obtained from th ese data. Two and three cylinder configurations of T/D = 1.0 were foun d to exhibit a cursory degree of similarity to a single, isolated impu lsively-started circular cylinder. Side-by-side configurations of T/D > 1.0 were dominated by the strong gap flow(s) between the cylinders, the vortices generated alongside the gap flow(s), and the formation of a single counter-rotating vortex pair in the far-wake. (C) 1997 Acade mic Press Limited.